Conventionally, in a multi-cylinder engine to be installed in an automobile or a like vehicle, there is known a technique, in which there are provided a hydraulically operated valve characteristic control device for controlling opening and closing timings of an intake valve and an exhaust valve depending on an operating condition of the engine, and a hydraulically operated valve stop device for stopping opening and closing the intake valve and the exhaust valve when the engine is in a low load condition so as to change valve characteristics and to perform a reduced cylinder operation by driving these devices for improving the fuel efficiency.
For instance, Patent Literature 1 discloses a technique, in which there are provided a hydraulically operated valve characteristic control device and a hydraulically operated valve stop device so as to change valve characteristics and to individually switch stopping/driving of exhaust valves by driving these devices. A valve stop mechanism disclosed in Patent Literature 1 is configured to switch flow of exhaust gas between a turbo-side exhaust passage and a bypass-side exhaust passage so as to quickly raise the catalyst temperature or to increase the supercharging pressure.
In Patent Literature 1, however, the capacity of an operating hydraulic pressure chamber (an advanced angle chamber and a retarded angle chamber) of a valve characteristic control device (VVT) is large. As a result, when operation periods of the valve characteristic control device and the valve stop device overlap each other, a hydraulic pressure to be supplied to the valve stop mechanism may be insufficient, which may lead to an inappropriate operation of the valve stop mechanism. The conventional art described in Patent Literature 1 is directed to switching between exhaust passages or to quickly raising the catalyst temperature, and fails to provide a solution to the problems as described above.